Method of making low noise film resistors and article

ABSTRACT

A method of forming a low current noise, thin film resistor having a thin electroconductive or resistive film applied to a dielectric substrate with a portion of the film thereafter being removed so as to increase the length to width ratio thereof. The method includes the step of rubbing, smoothing, or polishing the edges of the remaining film surrounding the area where said portion was removed with a rubberlike member whereby resistor current noise is significantly decreased.

United States Patent 2,564,706 8/1951 Mochel 338/308 1,962,438 6/1934 Flanzer et a1. 29/610 X 3,261,082 7/ 1966 Maissel et a]. 29/620 3,284,878 1 1/1966 Best 29/620 Primary Examiner-John F 1 Campbell Assistant Examiner-Donald P. Rooney Attorneys-Clarence R. Patty, Jr. and Walter S. Zebrowski ABSTRACT: A method of forming a low current noise, thin film resistor having a thin electroconductive or resistive film applied to a dielectric substrate with a portion of the film thereafter being removed so as to increase the length to width ratio thereof. The method includes the step of rubbing, smoothing, or polishing the edges of the remaining film surrounding the area where said portion was removed with a rubherlike member whereby resistor current noise is significantly decreased.

PATENTED JUL20I9J! 3, 594,679

IN VEN TORS. Robert 7. .Seay

Terry P. Smith A T TORNE Y METHOD or MAKING Low No sE FILM kEsIsToi ts AND ARTICLE BACKGROUND OF THE lNVENTlON creasing the resistance thereof to the desired value. The resistance of thin film resistors the film thickness or by thereof. b

The most common way of increasing the resistance is by increasing' the length to width ratio. Some prior art methods of tailoring the resistance included forming a photographic mask over the film and thereafter removing a portion of the film may increased by decreasing increasing the length to width ratio applied over the filma'nd thereafter a portion of both the resist and the. film are removed by sandblasting. Other methods include direct sandblasting of the film or removal thereof by passing high current through localized areas thereof.

It has been found that a'resistor formed in accordance with such methods has a resistor current noise of high value. As used herein, resistor current noise is defined as unwanted or undesired resistance fluctuations between the resistor terminals while a constant flow of current is passed throughthe conductive portion of said resistor within a frequency band, the value of the intensity of the disturbance being expressed in decibels.

SUMMARY OF THE INVENTION dielectric substrate, removing a portion of saidjfilm to increase thelength to width ratio thereof, and: thereafter rubbing, smoothing or polishing the edges of the remaining film sur roundingthe area where said portion was removed with a rubberlike member.

BRIEF DESCRIPTION OF THE DRAWING" FIG. 1 is a plan view of a dielectric substrate with a film re- I sistor applied thereon.

FIG. 2 is a plan view of the substrate and resistorof'FlG. 1 after the resistance value of the resistor has been adjusted.

FIG. 3 is a diagrammatic illustration of an apparatus by means'of which the cut edges of the r esistorfilm are rubbed and polished.

FIG.'4 is an oblique view of a film resistor formed in accordance with the method of this invention.

DETAILED DESCRIPTION In FIG. 1 there is shown a dielectric substrate having apto provide a method I vin V treatedby rubbing,

ide, tin oxide-antimony oxide, other modified tin oxide films or the like. Suitable dielectric substrate materials are glass, glass ceramics, ceramics, and the like.

The resistance of film I2 is adjusted or tailored as illustrated FIG. 2 by removing a portion thereof whereby the length to width ratio of the film is increased resulting in a resistor element [6 having a predetermined desired resistance. One suitable method for removing a portion of the resistive film is by directing a controlled sandblast stream of abrasive particles to the resistive film whereby the particles will abrade and remove the film in the path of the stream. The fiow of sandblast particles and movement of the emitting nozzle may be controlled by a controller which selected by one familiar with the art.

The cut edges of the resistive filrn surrounding the area where the portion of the film was removed is then furt e smoothing or polishing these edges with a 18. It has been found that such rubbing, smoothing, or polishing significantly decreases the current noise of. resistor element 16. The exact reason why this decreased current noise is achieved is not known, however, it

rubber-like member is believed to be as a result of removing the loose microscopic particles of resistive film which may not have been removed while the resistor was that such rubbing or polishing also smoothes these edges lessening the current noise-creating effect of any irregularities which may be found at the cut edges of the film. Rubberlike member 18 may be formed of natural or synthetic rubbers, such for example as those which may suitably be formed into erasers, or may be any soft resilient or elastic material suitable for polishing or buffing, such as plastics, felt, and the like. As in the case of an eraser, the rubberlike material may contain abrasiveparticles. Member 18 may be rubbed back and forth along the edges where the film was removed or may be rotated as illustrated in FIG. 3 by means of rotating device'20. Such a device maybe anordinary electric eraser motor or the like.

A typical example of carrying out the present invention is illustratedby the following. An electroconductive film of the type described in ,the heretofore noted Mochel patent, together with a pair of copper terminals in electrical contact with said film were applied to a hot-pressed alumina substrate. A sharp edge orifice nozzle was employed as a sandblast nozzle and was disposed above the electroconductive film at such a distance that the stream of particles to be emitted from the nozzle, would form a very thin controlled stream. The sandblast stream may comprise aluminum oxide powder and'dry air at a pressure of about 100 pounds per square inch. The nozzle was moved along the entire path for a distance sufficient to increase the length to width ratio of the electroconductive. film to a predetermined desired value. An' ordinary draftsrnans electric eraser was trimmed to a relatively small 1 diameter and caused to berubbed along the cut edges of the plied thereon an electroconductive or resistive film 12 which forrnsthe resistance element. Resistor terminals 14 are also applied on said substrate in electricalcontact with film 12. For one example of a suitable electroconductive film, its characteristics, and method of application, reference is made to US.

Pat. No. 2,564,706 issued to John M. Mochel. The electroconductive or resistive films suitable for the purposes of the present invention are hard metallic'oxide films such as tin oxfilm within the area where the film was removed while it was being rotated. It was found that the current noise value of such a device was decreased from 10 decibels to --30 decibels.

tron.

It not; it noted that the present method is suitable with is connected to terminals 14. When an .area of electroconductive film 12 has been removed sufficient being tailored. Further, it is believed FIG. 4 illustrates the completed device of the present inven- Although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such details be limitations on the scope of the invention except insofar as set forth in the following 7 claims.

We claim:

I. In the method of forming a low noise, thin film resistor comprising the steps of applying an electroconductive film having a resistance less than a predetermined desired value on a dielectric substrate, and thereafter removing a portion of said film to increase the length to width ratio thereof, the improvement comprising rubbing the edges of said film at the 

1. In the method of forming a low noise, thin film resistor comprising the steps of applying an electroconductive film having a resistance less than a predetermined desired value on a dielectric substrate, and thereafter removing a portion of said film to increase the length to width ratio thereof, the improvement comprising rubbing the edges of said film at the portion surrounding region thereof with a rubberlike member, so that current noise of said resistor is reduced.
 2. The method of claim 1 wherein said rubberlike member is composed of material selected from the group consisting of natural and synthetic rubbers.
 3. The method of claim 1 wherein said step of applying an electroconductive film comprises applying a hard metallic oxide film.
 4. The method of claim 3 wherein said step of applying a hard metallic oxide film comprises applying a tin oxide film.
 5. The article produced by the method of claim
 1. 